Currently available multiple use glucose sensing assemblies rely on a multiplicity of individual sensing elements, currently in the form of strips of coated paper, each one bearing electrical contacts. As multiple use glucose sensing assemblies become more common, the issue of the expense of the individual sensing elements used in these assemblies becomes an increasingly important issue. Currently available sensing assemblies that contain an array of single use sensors typically cost on the order of $0.80 per measurement. Over the years this expense can increment to a considerable sum. A serious health concern arises from this expense because a diabetic patient might refrain from taking a blood glucose measurement that he would otherwise take, due to the expense of taking the measurement. In some instances the failure to take a blood glucose measurement could be fatal. Moreover, the more measurements a diabetic patient takes, the better understanding she will gain of the relationship between her insulin injection schedule; her food intake, stress and exercise levels; and her blood glucose level.
A number of impediments, however, stand in the way of arriving at a truly economical multi-use sensing assembly. Assemblies that use chemical coated paper strips must be refilled with these strips.
Another type of assembly (a “coated wire assembly”) uses a wire having an electrochemically active metal (typically platinum) that is largely coated with insulation. A portion of this insulation is removed to form an electrode that is then covered with a assembly of membranes that produces an electric current when the analyte of interest (typically glucose) is present. In the production of a coated wire assembly it has been found that a problem is created in the removal of the wire insulation. With respect to insulated wires it has been found that the insulation is generally not applied in a truly concentric manner. Accordingly, if a laser beam is used to remove the insulation it tends to pit and stipple the electrochemically active surface of the wire, increasing its surface area. Although a large surface area is typically desirable, the process is unpredictable because of the unevenness of the insulation coat. As a result a non-uniformity is introduced into each set of sensing elements.
Another problem found in a coated wire system is encountered when a separate coated wire segment is used for each measurement. In this case, each coated wire segment must be carefully individually created by dip coating. Moreover, each individual coated wire segment must be brought into contact with body fluid, implying some means of retaining and moving the coated wire segments.
For a multiple use sensing assembly, because there is no calibration procedure, differing sensitivities at the various sensing sites result in a lack of repeatability in the formation of measurement and resultant inaccuracies.
Accordingly, a method of making a multiple use analyte sensing assembly that does not rely on chemical strips and that does not require the stripping away of an insulation layer from an underlying conductor is desirable.